This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Abstract Recently, we performed a miRNA expression profile using Microarray analysis in OA cartilage. We found the expression of miRNA-1 is undetectable while miRNA-31 is overexpression in the OA cartilage (154 fold increase) in comparison with the adjacent relative normal cartilage. Overexpression of miRNA-31 increases the expression of Indian Hedgehog (Ihh) and MMP-1 and 13 while knockdown miRNA-31 has opposite effects. Our data let us believe that Ihh plays a critical role in OA development. Our rationale for this focus is based on our and others'findings. Collective evidence include: a) Ihh is a key regulator of chondrocyte hypertrophy and endochondral bone formation [1] [2];b) Ihh is mainly expressed in the developmental growth plate, and it is almost undetectable in normal adult articular cartilage;c) excessive amounts of Ihh are synthesized by chondrocytes in OA patients;d) Ihh promotes chondrocyte hypertrophy and increases MMP production, which subsequently induces cartilage degeneration;e) Knockdown Ihh in cell culture results in suppression of MMP release. Our comparative study of normal and OA patients indicates that OA cartilage degeneration is accompanied by a chondrocyte response to this damage which involves enhanced Ihh synthesis. The increase of Ihh in OA may involve not only accelerated processes but also the initiation of events that are not ordinarily encountered in healthy cartilage. These findings support the notion that elevated Ihh signaling in the joint may contribute significantly to cartilage matrix degeneration in OA. However, direct genetic evidence for Ihh in OA has not been reported because tissue-specific activation of the Ihh gene (targeted by Col2a1-Cre) died shortly after birth. In this study, we will specifically delete the Ihh gene in chondrocytes in adult mice by generating Ihh conditional activated mice through Col2a1-CreERT2;Ihhfl / Ihhfl (provide by Dr. Beate Lanske, Harvard School of Dental Medicine) to confirm and extend these findings. Hypothesis: Inducible deletion of Ihh prevents cartilage degeneration in OA mouse model Specific Aim: We will determine whether disrupting Ihh signaling pathway in vivo will attenuate OA progression in Col2a1-CreERT2;Ihhfl / Ihhfl mouse OA model induced by surgery. Tamoxifen (TM) will be delivered intraperitoneally for 5 consecutive days to remove Ihh. The resulting changes in OA cartilage will be evaluated by X-ray and histologically by Safranin-O staining, and quantified using the Modified Mankin score. Expression of type II, IX and X collagens and matrix metalloproteinase (MMP), -3, -9, and -13 will be further examined by immunohistochemistry and in situ hybridization (ISH). The change of cartilage degeneration will be monitored using MMPSense probe in vivo by fluorescence-based quantitative tomography, a non-invasive in vivo imaging technique (VisEn Medical). Summary Ihh expression is markedly elevated in OA cartilage. We further demonstrate that Ihh promotes chondrocyte hypertrophy and induces the release of matrix metalloproteinase in vitro. Thus, Ihh may activate cartilage catabolism during arthritis. In this application, we propose to evaluate novel strategies for prevention of Ihh induced cartilage degeneration in arthritis by the direct reduction of Ihh in vivo.